A communication system, such as the Wideband Code Division Multiple Access (WCDMA) system described in documents from 3rd Generation Partnership Project, may provide unicast, multicast, and/or broadcast services. The multicast service provides point-to-multipoint communication between a base station and a group of wireless devices, called User Equipment (UE) devices. A broadcast service provides point-to-multipoint communication between the base station and all UE devices within a certain broadcast area. Some examples of multicast and broadcast services are news, data, subscribed, and push-to-talk services. The broadcast and multicast services, called Multimedia Broadcast and Multicast Service (MBMS) may send data to the UE devices sporadically, periodically, or continuously.
The communication system preferably sends control information, configuration information, etc. for the MBMS supported by the system. The signaling is sent on a control channel called MBMS Control Channel (MCCH). A UE device receiving one or more services would then monitor the MCCH for signaling sent for the service(s) being received. The UE device may operate in an idle state whenever it is not actively exchanging data with one or more base stations in the system. In the idle state, the radio receiver with its path searcher and other power demanding means is mostly in an off state to save power, but the UE device wakes up periodically to receive e.g. paging messages from the system, and then again powers down as much circuitry as possible in the remaining time in order to conserve battery power.
In WCDMA, an MBMS Indicator Channel (MICH) is used to send MBMS notification indicators that indicate whether messages are being sent on the MCCH. The MCCH is carried in a Secondary Common Control Physical Channel (S-CCPCH). The messages sent on the MCCH contain information that allows the wireless devices to receive an MBMS Traffic Channel (MTCH). Such information may indicate, for example, which services are active, how to decode the MTCH, whether soft combining is possible, etc. The MTCH is a transport channel that carries traffic data or content for the services.
Each multicast/broadcast service is assigned specific notification indicators, which are set to ‘1’ whenever messages are being sent on the MCCH for the service. Each UE device monitors the notification indicators for all of the services desired by the UE device. Whenever the notification indicator for any desired service is set, the UE device further processes the S-CCPCH to look for messages sent for that service.
Further, in WCDMA, a Page Indicator Channel (PICH) is used to send paging indicators to UE devices in idle state. The paging indicators for each idle wireless device indicate whether messages are being sent on a Paging Channel (PCH) for the UE device. The PCH is a transport channel that is also carried in the S-CCPCH. Each idle UE device monitors the PICH for its paging indicators. If these paging indicators are set to ‘1’, then the wireless device processes the S-CCPCH to look for any messages sent for the wireless device. A key characteristic of indicator channels such as the PICH and MICH is that the information carried on these channels is short and un-coded and can thus be received and interpreted very quickly. Paging indicators for each idle wireless device are sent on the PICH in paging occasions for the wireless device. The notification indicators for each service are sent in each frame on the MICH and are set to the same notification value, either ‘1’ or ‘0’, for the entire modification period. The modification period may represent a time interval in which critical signaling information, which is information that is needed in order to receive MBMS content, may be changed.
The modification period is selected to be sufficiently long so that all UE devices can reliably detect at least one notification indicator sent on the MICH during the modification period. A wireless device with a Discontinuous Receiving (DRX) cycle that is shorter than the modification period can read the MICH during its paging occasion in each DRX cycle. A wireless device with a DRX cycle that is longer than the modification period can wake up between paging occasions to read the MICH. The modification period may be selected to be equal to or greater than a predetermined minimum duration so that wireless devices with long DRX cycles do not need to wake up too frequently. Depending on how the DRX cycle and the modification period are configured, a wireless device may be able to read one or multiple notification indicators for each desired service in each modification period.
In reality, there are some complications to achieve good performance of detecting the notification indicators. As in other wireless systems, there are always a risk of missing detections and get false alarms due to bad propagation conditions, low power in received signals, high interference, or high noise. In addition, there is a special issue with MICH detection; there is a risk for notification indicator collision when notification indicators from different MBMS services have overlapping positions in a MICH frame. It is therefore a desire to increase robustness in detection of notification indicators while keeping the power consumption low.
EP 1 608 196 A1 discloses a method for detecting notifications in a communication device. The method comprises the steps of successively receiving a finite set of notification indicators form a communication network, which in combination represent a notification identifier associated with the device; subsequently checking each received notification indicator whether it is positive or negative; determining, after each checked notification indicator and based on the checked notification indicators, whether to proceed with the next notification indicator or to decide on a presence of a notification for the predetermined notification indicator; and, if it is determined that a decision is to be made, interrupting the checking of notification before all notification indicators of the set have been checking and deciding, based on the checked notification indicators, whether a notification for the predetermined notification identifier is assumed to be present or not.